In the prior art, various solar battery modules and solar battery panels have been implemented in practice that incorporate solar cells installed in a window material capable of transmitting sunlight. Generally, these are silicon type solar battery modules (or panels) that are made by laying flat plate shaped silicon solar cells that are manufactured from wafer shaped silicon crystals between two glass plates. Such a module is an adhered structure that is made by lining up the solar cells in a planar configuration with appropriate gaps being left between them and electrically connecting the cells by ribbon shaped conductors, and then by embedding them using an EVA (ethylene vinyl acetate) resin in the gap between the two glass plates.
Furthermore, there is a thin layer type of solar battery module in which are made from amorphous silicon and microcrystalline material. In order to manufacture such module as a window material, first, a transparent electrode layer of TCO (SnO2) is formed on a glass board substrate, and is separated into sections by laser light for making cell electrode portions. Next, a thin silicon layer, amorphous silicon (a-Si), and a thin silicon microcrystal layer are sequentially laminated thereupon, and this photoelectric layer is separated into sections at a constant pitch by laser light. Furthermore, a thin metallic layer is adhered over the entire area of the rear surface as an electrode, and, again with laser light, this metallic layer is separated into mutually insulated portions, so that a large number of small thin-layer solar cells are electrically connected in series at one time.
With these solar battery modules described above, only one side of the solar cells can serve as a light reception surface, and the electricity generation capability is low because the usable range of the ambient light around the module is narrow. Furthermore, with a silicon type solar battery module, the sunlight transmission ratio (see-through ratio) become small due to the flat plate type solar cells of large size. Moreover, with a thin layer type solar battery module, manufacturing the thin layers on the glass substrates is accompanied by many difficulties.
Thus, in consideration of the above problems, the inventor of the present application has proposed a spherical solar cell as described in Patent Document #1. This spherical solar cell consists of a p type or n type spherical semiconductor of diameter 1 to 2 mm, a pn junction formed in the vicinity of the spherical surface of the semiconductor, a pair of small positive and negative electrodes provided at opposite ends of the surface of the spherical semiconductor so as to oppose one another with its center interposed between them. As compared to the silicon type solar cell or the thin layer type solar cell described above, this spherical solar cell is compact, and can be manufactured easily at a low price.
Since the surface of the spherical solar cell is a spherical surface, its technical advantages become remarkable in an environment in which there is a lot of reflected light or scattered light as well as the directly incident light. For example, if it is embedded in a transparent package, reflected light and scattered light in the interior can contribute to electricity generation; and, if a solar battery module that is combined with a window is installed vertically on a building such as an office building or the like, then it can generate electricity due to absorption of reflected light from the ground surface or the surroundings of the building or the like.
Although the incident direction of the direct incident light from the sun changes along with time as the angle of incidence changes, since the light reception surface is shaped to be spherical, it is still possible to anticipate comparatively stable generation of electricity without dependence on the incident direction, as compared with solar cell of a planar type.
Furthermore, as described in Patent Documents #2 and #3, the inventor of the present application has proposed a see-through type solar battery module, in which spherical cells as described above are arranged in a matrix configuration having a plurality of rows and a plurality of columns, are connected in parallel and in series by thin flexible lead wiring or printed wiring, and are molded in transparent resin between a pair of transparent case plates.
Patent Document #1: International Publication WO 98/15983.
Patent Document #2: International Publication WO 03/36731.
Patent Document #3: International Publication WO 2007/80631.